Contemporary gas turbine fan and compressor blade designs lead to high stage loading on low aspect ratio airfoils. These blades experience chordwise vibration at lower frequencies than previous blading. Thus, the potential for resonance crossings occurring at high engine speeds and consequently high energy increases, and can cause significant high cycle fatigue problems. These can result in liberation of portions of the airfoil.
Earlier design philosophies to overcome such problems included the incorporation of mid-span shrouds and tip shrouds to increase the chordwise stiffness. This also increased the system mechanical damping level. Other approaches are those such as shown in U.S. Pat. No. 4,118,145 issued Oct. 3, 1978 which incorporate composite reinforcement to portions of the airfoil tip section to strengthen it against chordwise "strip" modes of vibration.
Hollow blades are preferred in modern engines because of the light weight, but these blades have increased vibration problems.